Globally valid relations converting magnitudes of intermediate and deep-focus earthquakes to MW

Abstract

An essential step in the compilation of homogeneous and complete earthquake catalogs is the thorough investigation of potentially robust relations between different magnitude scales. The vast majority of already published relations usually concerns shallow-focus earthquake data with depths up to 60-70 km. In the present study, several magnitude scales reported by 66 world-wide data providers in conjunction with published catalogs are examined within the depth range of 61-700 km, by applying least-squares regression analysis. Among other widely used scales, as body wave (mb, mB) and surface wave (Ms) magnitudes cited by International Centers (i.e. ISC, NEIC and IDC), the behavior of relevant magnitude scales determined by MOS (Moscow, Russia), BJI (Beijing, China), DJA (Djakarta, Indonesia) and the Japanese magnitude calculated by JMA, is also examined. By this way, robust calibrating relationships of 12 magnitude scales to the moment magnitudes provided by GCMT, NEIC and JMA are defined. From the obtained results important observations on the behavior of certain magnitude scales were made. Thus, a remarkable variation of mb scale cited by IDC could be noted for intermediate and deep focus events. Furthermore, a comparison with the Mw of NIED revealed an apparent lower “saturation” level around 5.0 below which the moment magnitude values published by GCMT and NEIC, are systematically overestimated.